Vacuum pumps



y 13, 1969 P. PEGON 3,443,743

VACUUM PUMPS 4 Filed Nov. 15. 1966 Sheet 0r a FIG.]

Ma 13, 1969 P. PEGON 3,443,743

VACUUM".PUMPS Filed Nov. 15. 1966 Sheet 3 or a P. PEGON VACUUMiPUMPS May13, 1969 Sheet Filed Nov. 15. 1966 3,443,743 VACUUM PUMPS Pierre Pegon,Paris, France, assignor to Societe Clover, Villejuif, Val-de-Marne,France Filed Nov. 15, 1966, Ser. No. 594,563 Int. Cl. F04f 9/02 US. Cl.230-101 2 Claims ABSTRACT OF THE DISCLOSURE A vacuum pump which uses thepumping fluid from an outside boiler to drive molecules of gas from achamber, compressing them by successive stages with the fluidcirculating through a piping system having orifices known as ejectorsspaced from cooled condensation plates within said chamber withindependent heating adjustment in the parts of the piping system.

The present invention relates to vacuum pumps, and more particularly tovacuum pumps of the ejection and diffusion type, with association ofejectors and condensing surfaces.

The invention has mainly for its object to provide a certain flexibilityin the mounting and association of the ejectors and condensing surfaces,while at the same time clearly separating the functions of: boiling,ejection, condensation, of the vacuum pump so as to be able to provide aseparate control of the parameters which govern the operation of thesemembers.

The design of the form of a pump according to the invention permits:

of its simple adaption to a given particular problem or to a vacuumchamber considered;

of improving the safety of operation of pumping;

of reducing the overall size for a maximum depression;

of facilitating the mounting of the pump in the interior of a vacuumchamber.

These general results are obtained by means of the following specialarrangements of the fluid circuits:

The pumping fluid which drives the molecules of gas from the chamber andcompresses them by successive stages up to a primary vacuum stage,circulates inside tubes or piping systems provided with orifices knownas ejectors. The tubes are provided with independent heating which keepsthem at a temperature which can be adjusted at will. Thus, thetemperature of the vapour at the level of an ejector is not, as in theprior art, the result of a complex equilibrium which is influenced byall the factors of the data of the apparatus and on which it is notpossible to act directly, as is the case with known pumps. In addition,by acting locally on the cross-section of the passage of the distributortubes, the flow-rate of the vapour is controlled. With the pipingsystems which bring the ejectors to a predetermined temperature, thereare associated cooled condensation plates, over the faces of which flowsthe pumping fluid, which is subsequently collected and returned to theboiler. The curved lines which indicate the piping of the ejectors arelocated at a constant distance from the adjacent condensation plates.The piping systems of the ejectors are grouped together in differentstages of pumping and the corresponding condensation plates form apumping unit. This pumping unit which is subsequently multiplied after anumber of translations or rotations, constitutes the pump itself.

The boiler is separate from the pump proper; it heats the fluid to adesired temperature which determines the vapour pressure. At the outletof the boiler, valves are ntted States atent O" 3,443,743 Patented May13, 1969 provided on the various pipes which permit the boiler and thethermal inertia to be completely isolated.

Other characteristic features and advantages will be brought out in thedescription which follows below, reference being made to theaccompanying drawings which illustrate, purely by way of indication butnot in any limitative sense, one form of application of the invention.

In these drawings:

FIG. 1 is a view in cross-section of a cylindrical secondary pumpaccording to the invention.

FIG. 2 is a view in cross-section of an alternative form of theinvention, applied to the evacuation of a metallurgical crucible undervacuum.

FIG. 3 is a view in cross-section of another alternative form, in whichthe modular vacuum pump is contained in the chamber of which it ensuresthe pumping.

FIG. 4 is a partial section taken along the line IV--IV of FIG. 3.

There is shown in FIG. 1 a pump in which, by carrying away molecules ofgas from the opening 3 of the pump, a fluid 4 produces a high vacuum inthe chamber 2. The boiler 5 sends vapour 4 into the pipes 6 heated to apredetermined temperature.

These pipes 6 are connected to ejection pipes 7 through the intermediaryof couplings 8. These pipes are also heated to a pre-determinedtemperature and they are provided in places or continuously withorifices which constitute the ejectors proper 9.

Although other fluids may equally well be employed in a pumping systemaccording to the invention, in the example chosen here, oil vapour hasbeen adopted. In this case, it is advantageous to use glass pipescarrying the ejectors. A conducting deposit having the function of aheating resistance 10 is deposited on this glass by conventional means.

The outgoing conduits 6 are heat-insulated, the vacuum-tight passage 11is insulated electrically from the casing 13 of the pump, and theheating means for the pipes 6 and the pipes 7 are connected togetherelectrically in known manner.

It is known that in conventional diffusion pumps, the vapour reachingthe ejection orifices is frequently humid, that is to say it containssmall droplets of fluid; these droplets have a low speed which slowsdown the speed of the vapour and they serve as condensation nuclei forthe vapour which is cooled by depressurisation. The phenomenacontributes to reduce the performances of conventional pumps, and inaddition droplets are frequently deposited on the lips of the ejectorsand are then re-evaporated, thus forming a substantial back-flow.Finally, in conventional diffusion or ejection pumps, the temperature ofthe ejectors is the result of a complex thermal equilibrium of the wholeunit, the only pro-adjusted parameters being, in this case, the heatingof the boiler and the flow-rate of water into the cooling conduits whichsurround the pump body.

The vapour passing out of the ejectors converts its pressure energy tokinetic energy, and it carries away the molecules of gas in thedirection of its movement, which results in a pressure gradient. Afterhaving played its part of mechanical impulsion, it is important that thevapour should be condensed as rapidly as possible. When the molecules ofvapour have played their part of carrying away, that is to say when theyhave lost the coherence of their movement, they become harmful to theeffectiveness of the pump. The efiiciency of the pump is in factdiminished by the oil vapour pressure in the compressed zone, since itis in fact necessary to impart to it a momentum so as to maintain it inthis zone. The efficiency is also reduced by the back-flow which isformed by the rebounding of the oil molecules from the mechanical partsof the pump.

Thus, all these parts of the pump will be very strongly cooled and themolecules will be condensed by associating with the cooled pipes 7carrying the ejectors 9, large cooled surfaces forming the casing 13 ofthe pump and plates 12 inside the pump. These surfaces are cooled byconduits 14. The oil is condensed on these surfaces, trickles down andis collected in a tank 15. It is taken-up by a pump 16 and returned tothe boiler 5.

It will be recalled that in conventional ditfusion pumps or ejection(booster) pumps, the body of the pump is cooled; on the other hand, dueto the very design of these pumps, the intake chimneys of the vapourcannot be cooled; these chimneys constitute the internal structures andare directly connected to the boiler. According to the invention, on thecontrary, the condensation surfaces are multiplied, and the associationof the ejection pipes and the cooled plates permits remarkablecompactness of the pumps to be obtained.

This is particularly illustrated in FIG. 1, in which, in a pump havingan external shape which is generally that of conventional pumps, twoadditional pumping stages, of which one is a booster stage, are locatedin the space usually reserved for the vapour-intake chimneys. Followingthis arrangement in accordance with the invention, the pumping rate isincreased and the critical starting pressure is raised.

The possibility of distributing vapour in the independently-heatedconduits 7 which carry the ejectors 9, and the association of theseconduits with the cooled surfaces 12 are two factors which make itpossible to modify the usual structure of the pumps with great freedom.

This can be seen from FIG. 1 when looking at the interior of the pumpbody 1 below its secondary valve 22, and it is seen in particular inFIGS. 2 and 3 which will be described later.

As distinct from conventional pumps, in which the boiler is intimatelyassociated, if not incorporated in the pump body, the boiler accordingto the invention is in this case separated from the pump proper 1. Itcan be isolated from the oil recovery tank and from the distributionconduits 6 by closing the valves 18 and 19. This boiler is coupled to aprimary pumping unit by the pipe carrying the valve 17.

As the boiler is treated as a separate unit, its temperature does notaffect the thermal equilibrium of the pump, which permits a considerablefreedom of action in the choice of the method of heating. This fact,associated with the presence of long distribution conduits 6 and 7permits achieving elimination of the disastrous repercussions oferuptive boiling on the pumping speed.

In addition, in order to stop the secondary pump, it is only necessaryto close'the valves 18 and 19, and after a few seconds, air can beadmitted to the interior of the pump which does not contain any hot oil.This constitutes an appreciable advantage as compared with conventionalpumps.

The pump shown by way of example in FIG. 1 comprises four pumping stages24, 25, 26 and 27. The stages 24, and 27 are supported on the internaledge 28 of the cylindrical part of the pump; this is also the case forthe cooling plate 121) and the ejection trumpet 31. The stage 26together with the cooling plate 12a and the ring 33 which acts as anejection trumpet, are supported on the removable lower portion 34 of thepump. These various parts are centered with respect to each other. Thecondensation oil flows into the tank 15 either through the interior ofthe ejection booster or through. a pipe 35 and the flexible coupling 29.

FIG. 2 illustrates a special application of the principles previouslydescribed to the constructions of a vacuum furnace located in theinterior of the secondary pump which is itself incorporated in theinterior of the chamber.

The pumping fluid 4 which effects the vacuum by carrying away themolecules of gas from the chamber 30, from the opening 31 of the pump4', is conveyed from the boiler 5 by means of conduits 6 heated to agiven temperature. These pipes are connected to the ejection pipes.

7 through the intermediary of couplings 8; these pipes 7 are also heatedto a given temperature and are provided locally or continuously withorifices 9 forming ejectors. On the pipes 7, there has been shown aheating resistance 10. The pipes 6 are thermally insulated. Theelectrical heating connections between the conduits 6 and 7 have notbeen shown in detail, and this also applies to the vacuum seal 23.

The pumping fluid condenses on the cooled surfaces 12 which have a watercirculation system 63. The oil trickles down over the surfaces and iscollected in a cooled tank 15 through the intermediary of a conduit 35having a flexible coupling 29 to facilitate assembly. It is taken-up bythe pump 16 which sends it into the boiler 5. The boiler, the tank, thesecondary pump and the chamber are connected to a primary pump (notshown) through the piping systems 20 and 21. The valves 17, 18 and 19enable the boiler to be isolated; the valve 36 isolates the chamber fromthe primary pumping circuit, and finally the valve 37 on the primarycircuit and the annular valve 32 permit the secondary pump 4 to beisolated.

The secondary pump shown in FIG. 2 comprises three stages 24, 25 and25'. It is also provided with a cooled baflie 38, moved by the piston 39passing through the cover 40 of the vacuum chamber. The cover 40 of thevacuum chamber shown in FIG. 2 pivots about the shaft 41 and is clampedon the body of the chamber, before pumping, by means of the nut 42. Itcontains a crucible 43, a heating device 44, the electrical connectionof which is shown at 47, radiation screens 45 and supports 46. All thisequipment is known and does not require any more detailed explanation.

In order to pump the chamber to the primary vacuum, the valves 36, 37and 17 are opened to communicate respectively on the chamber, thesecondary pump and the conduit 6, and on the boiler. The starting-up ofthe secondary pump can then begin. The valve 17 is closed and then theheating element 68 of the boiler is switched on together with theheating resistances of the pipes 6 and 7; finally the valves 19 and 18are opened. The fluid circulates in the pipe 6 and reaches the ejectors9. In order to pump in secondary in the chamber, the secondary valve 32is then opened. The pump 16 for returning the oil from the tank to theboiler is controlled by a level reference located in the boiler. Inorder to cut off all secondary pumping, it is only necessary to isolatethe boiler by closing the valves 19 and 18. FIGS. 3 and 4 areillustrations of an alternative form in which the portion which carriesout the pumping is located inside the chamber, the boiler and the returntank being mounted outside the chamber.

A boiler 5 sends vapour 4 into conduits 6 heated to a controlledtemperature. This boiler is connected to a primary pumping set (notshown) through the intermediary of the conduit 20, and to a return pump16 coupled to the tank 15. Various valves 19, 17 and 18 enable thisboiler to be isolated. After having passed through the chamber 2', thepiping system 6 extends to the pipes 38 and 37, then by means ofconnections such as 8, pass the ejection piping 7' which carry theejectors. These latter are arranged vertically. There have been shownthe ejectors 9 and also a heating resistance 10. As in the previouscase, all these piping systems are brought up to a definite temperature.

With the vertical ejectors are associated cooled vertical plates 12, theshape of which is shown in FIG. 4. The cooling circuit 63 passes throughthe chamber 2' and then supplies two horizontal racks 45 and 46, towhich the cooling circuit of the plates is connected at points such as47 and 48.

The plates have been designed in such manner that by symmetry andrepetition a pump is obtained which has a very large suction surface.The pump is constituted by a modular assembly of ejection piping andplates; it opens into the chamber at two opposite faces.

The oil streaming over the cooled faces is collected by gravity on theflow surfaces 52 and thence passes into two collectors 49 which arejoined together at 53. The flow continues through the pipe 55 down tothe tank 15 after having passed through the chamber by the passage 54.

There has thus been shown a four-stage pump, the last stage of whichcompresses the gas to a primary vacuum pressure. The gas is then pumpedby means of the collector pipes 49 and then the pipe 55 carrying thevalve 56 and then the tubular coupling 21, by a primary pumping set (notshown). The pump is provided with a cooled cover 57 and a bottom 58, andrests on feet 59. It is advantageous to group all the vacuum passages(water, oil heating resistances) together on a single flange 60. Nosecondary valve has been provided on this secondary pump.

It will of course be understood that the present invention has beendescribed above purely by way of explanation, and that any modificationof detail may be made thereto in conformity with its general outlinewithout thereby departing from its scope.

I claim:

1. A vacuum pump comprising a chamber to be evacuated,

ejection pipes within said chamber having electrical heating resistancesthereon,

a boiler located outside said chamber for producing a vapor andconnected to said ejection pipes by tubes having heating means for saidtubes,

condensation plates within said chamber and located on opposite sides ofsaid ejection pipes having a shape of converging walls in two oppositedirections with a section view through said walls substantially in asinusoidal wave 'form, said plates having a cooling means for coolingsaid plates,

said ejector pipes parallel to said condensation plates and constitutingstages from the point of wider separation of said converging walls tothe point of lesser separation forming a throttled portion,

and exhaust means connected to said chamber,

whereby vapor from said boiler passes with controlled temperaturethrough said tubes and through said ejection pipes and carries awaymolecules of gas from said chamber to be evacuated.

2. The pump of claim 1, further characterized by said ejector pipes eachhaving a rectilinear shape opening toward said throttled portion of saidconverging walls.

References Cited UNITED STATES PATENTS 2,150,685 3/1939 Hickman 23010*12,608,343 8/1952 Colaiaco et al. 230-101 2,899,127 8/1959 Power 230 l012,975,957 3/1961 Geller et al 230 101 X 3,144,756 8/1964 Arnold et a123010'1 X 3,203,624 8/1965 Smith 230 101 3,245,609 4/1966 Rangabe230-101 X 3,326,451 6/1967 Gaydou 230-101 X 3,332,608 7/1967 Landfors230-401 3,344,979 10/ 1967 Chester 230101 DO-NLEY I. STOCKING, PrimaryExaminer.

WARREN I. KRAUSS, Assistant Examiner.

